Roller spearguns

Quote from parker

I'm interested to learn more about this!

Me too! No-hole rubbers sound very interesting!

Also, I think that reduced muzzle flip in the roller is mainly due to the fact that the rubbers are stretched parallel to the shaft when loaded, thereby channeling recoil directly backwards, towards the handle (as opposed to diagonally, with angled bands).
Closed muzzle euro's with a single band (parallel to shaft) would also show very little muzzle flip, and reduced recoil if ballasted properly (and if the design of the handle channels recoil to the palm of the hand effectively).

PS, I haven't tried a roller as of yet, but for our conditions, a simple single or double banded gun works well for me

Quote from Dan

You guys are insatiable. Charlie goes out of his way to settle the argument and it's not enough. If floppers bother you for a penetration test then take the floppers off, build the guns yourselves and test again. But it will not change the results.

Charlie, I admire the spirit with which you approached this whole endeavor. I'd like to thank you for the effort with a pair new Speardiver Platinum no hole rubber bands. Just let me know the length and diameter 14mm or 16mm. Keep in mind they're more powerful than the conventional bands with a hole so as not to overpower your gun.

Huh, are you serious? How do you tie in the wishbones? Does that mean no water intrusion? That would be nice.

Can you make a set for my roller gun?

Charlie

Dan,

How do you tie in the wishbone in your new bands? And what's the max stretch ratio you can cut them to?

I like the concept very much. Smaller bands, more power.

:popcorn3:

Quote from Chase

Dan,

How do you tie in the wishbone in your new bands? And what's the max stretch ratio you can cut them to?

I like the concept very much. Smaller bands, more power.

I am pretty sure Dan was kidding!

--22" band-2" wishbone - 22" band - 3" wishbone --

Basically a loop. I use 5/8" bands.

Thanks.

Charlie

Have you had a chance to shoot them yet? What band stretch ratio can you cut them to?

Just looking back on something seal said about rollerguns way back in post #145.

"The idea of the pulleys is to break the speed limit of normal bands. Every shaft has a limit that can be accelerated to with normal bands. Even if you store five time more energy in multi bands configuration, you will give to the shaft only a small part of it, the rest will go for recoil and drag."

On reflection I think what seal is saying is that the rollergun's more gradual acceleration allows shafts of reduced diameter to be shot that would not be possible with a conventional gun as the latter gun's shorter and more brutal acceleration would load up the thinner shaft too quickly causing the shaft to bend and thus adversely affect the shot. Both gun types can store and deliver the same energy, but the rollergun can deliver it with less likelihood of overpowering the spear, although the extra margin gained will probably have a limit. If you shoot spears of a diameter that are able to take the acceleration then a rollergun and a conventional gun should deliver the same results, all other things being equal, as it is not about energy storage or gun efficiency but what the spear can absorb and how fast and how far you need to send it to disable what lies at the other end.

Running the comparison calculations using a diagrammatic approach.

Quote from popgun pete

Just looking back on something seal said about rollerguns way back in post #145.

"The idea of the pulleys is to break the speed limit of normal bands. Every shaft has a limit that can be accelerated to with normal bands. Even if you store five time more energy in multi bands configuration, you will give to the shaft only a small part of it, the rest will go for recoil and drag."

On reflection I think what seal is saying is that the rollergun's more gradual acceleration allows shafts of reduced diameter to be shot that would not be possible with a conventional gun as the latter gun's shorter and more brutal acceleration would load up the thinner shaft too quickly causing the shaft to bend and thus adversely affect the shot. Both gun types can store and deliver the same energy, but the rollergun can deliver it with less likelihood of overpowering the spear, although the extra margin gained will probably have a limit. If you shoot spears of a diameter that are able to take the acceleration then a rollergun and a conventional gun should deliver the same results, all other things being equal, as it is not about energy storage or gun efficiency but what the spear can absorb and how fast and how far you need to send it to disable what lies at the other end.

Yes first thing is righ,but its also about the Efficiency.The gradual and longer transfer of energy is more efficient not only becouse of the lack of shaft bending but mainly becouse of lack of recoil.
This is so simple that I hope more people will understand now: Everybody admit that rollers has no recoil-well if you can measure this lack of lost energy,then add it to the energy of spear,becouse it goes there.
Another benefit is that lack of recoil improves accuracy and aiming.
And believe me the recoil of spearguns is signifficant value becouse guns are signifficantly light compared to the heavy spear-bullet. Especialy most pipeguns,their spears are only double lighter than the gun itself.Even the wood guns where this relation could be 3 to 5 : 1 ,its still not enough.
So not only the gun shoots the spear,but the spear shoots the gun back with quite big value of energy.
In compareson the relation of a riffle mass to its bullet is arrownd 200:1

Quote from seal

Yes first thing is righ,but its also about the Efficiency.The gradual and longer transfer of energy is more efficient not only becouse of the lack of shaft bending but mainly becouse of lack of recoil.
This is so simple that I hope more people will understand now: Everybody admit that rollers has no recoil-well if you can measure this lack of lost energy,then add it to the energy of spear,becouse it goes there.
Another benefit is that lack of recoil improves accuracy and aiming.
And believe me the recoil of spearguns is signifficant value becouse guns are signifficantly light compared to the heavy spear-bullet. Especialy most pipeguns,their spears are only double lighter than the gun itself.Even the wood guns where this relation could be 3 to 5 : 1 ,its still not enough.
So not only the gun shoots the spear,but the spear shoots the gun back with quite big value of energy.
In compareson the relation of a riffle mass to its bullet is arrownd 200:1

Well efficiency is going to depend on how you define it as in a two-stage loading rollergun the preload never gets used for shooting, so the energy stored there is thrown away when the gun is reloaded each time for the next shot. Thus there is a difference between energy used for shooting and the energy stored in a gun. You could say a more efficient speargun uses all its energy for the shot, which is what you have with a conventional band gun (not counting the energy lost as the band tension drops as the bands slightly relax over time when cocked). Your own cable rollergun has the preload built-in when you assemble it as you use single-stage loading and therefore you use all the energy provided by cocking the gun for the next shot, hence it is a different type of weapon compared to the usual rollergun. Add to that the sub-pulley drive which allows only the upper end of the band energy to be delivered over the full length of the top deck, however that extra hardware of moving cables and pulleys has to take energy to move them and you lose efficiency there, not gain it.

What we should be talking about is effectiveness rather than efficiency as mechanically rollerguns have to be less efficient than a conventional band gun, but the rollergun has a better power distribution. Power is defined as the rate of doing work or using energy, in the conventional band gun all that energy is imparted to the spear right at the beginning of travel, whereas in a rollergun it is delivered all the way along the top deck until the spear reaches the muzzle, like in a pneumatic speargun. Hence if the gun is not ballasted sufficiently then the nature of the recoil can make a conventional band gun less manageable to hold steadily for aiming compared with the rollergun which provides less of a jerk when it shoots as the power is applied more gradually to the spear and consequently the gun. High grip, rear handle euroguns are usually not ballasted, but the bands are matched to the spear to make them more manageable for shooting with a straight arm position. If you are pushing the margins of energy storage and power delivery then the rollergun can handle it better, but at the necessity of a broader weapon which may or may not be a disadvantage depending on what you are using it on in terms of the maneuvering required to bring the gun onto the target or the likely track of the target as it swims towards the anticipated flight direction of the spear from the gun.

Energy released for the shot is divided between user and gun, as a combination, and the projectile with respect to their respective masses, regardless of whether we are talking firearms or spearguns and bullets or spears. The gun and user are not rigidly coupled together, so the user has to resist the gun moving with respect to himself and the rollergun's recoil is easier to manage as it loads up the diver's arm (or arms) less rapidly than with a conventional band gun. When a speargun is fired the diver and gun are both pushed back in the water and the recoil we perceive is how well we and the gun are coupled as a single unit when that movement occurs. We don't see ourselves being pushed back in the water, but that is what happens. Incidentally if a gun is braced against the wall of pool in a test shot then the results are distorted as now the "user" is the pool and the weight of the Earth if it is an in-ground concrete pool! Rollerguns certainly have some recoil as I was watching some sea experiments on video with a mid-handle rollergun, the only way the gun would shoot accurately was with an arm brace to better couple the user and gun together as a unit.

Interestingly when that same rollergun was fitted with thicker bands in the pursuit of increasing the range for a kill shot the spear had less performance when striking a foam target than it had before with weaker bands and my guess is the bands were now so strong that they could eject the spear from the gun with just the band stretch in the top deck, i.e. before the roller system got working and the bands had released all their stored energy for shooting. When a heavier spear (10 mm!) was substituted in the gun the performance improved as evidenced by greater spear penetration at the foam target, so like all spearguns the bands and the spear had to be matched with a combination that did not over power nor under power both the gun and the spear for stable flight of the latter to the target.

I really enjoyed that read popgun Pete

Ok. Now I want to know more about those "no-hole" bands. :rolleyes1:

Theories... if it was better it would be the standard. Like I said, it fills a niche for a specific target market. If you like it, great. But your beating a dead horse. You're never going to win over everyone so just keep shooting whatever you like. :thumbsup2:

Quote from Chase

Theories... if it was better it would be the standard. Like I said, it fills a niche for a specific target market. If you like it, great. But your beating a dead horse. You're never going to win over everyone so just keep shooting whatever you like. :thumbsup2:

Not theories,but Practice.I dont want to win over everyone,just thought my experience could be usefull to people who are dedicated to our sport

Here is something to think about. If we take a single rubber band and wishbone assembly, pull it back on a gun to the rear tab or wishbone notch position and then let it go without engaging it on the shaft then the band zips forwards on its own at the maximum velocity it can achieve. Once we add a shaft for the band to pull along behind it then the band is slowed down and the heavier the shaft is then the slower the band can contract. Logic would suggest that if we add more bands of the same type to the spear then the bands individually have less mass to pull along as their share of the load and the band contraction velocity of the band group will increase, but at some point if sufficient bands have been added then the velocity limit will be when the bands once more reach their zero load contraction velocity. The contraction velocity will not really be at "zero load" as there will be hydrodynamic drag on the bands and the wishbones, but it will be what they experience when used in a speargun underwater. However the question would be whether bands can ever reach that limit on a practical speargun before the axial drive on the shaft started to buckle the spear.

If there is an advantage to some rollerguns then it must be related to the hydrodynamic drag effects as there are less wishbones and band surfaces, particularly the cut-off ends of the bands being pulled through the water for the same amount of energy stored in the bands, but at what magnitude of wishbone velocity do these effects become significant? One interesting feature of the sub-pulley cable rollergun drive system is the wishbone engaging the shaft travels at twice the velocity of the cut-off band ends, but the bands are slowed by having to pull the spear via the folded cable drive, so the system is not a simple band contraction speed multiplier. However drag effects related to velocity would be different for the wishbone than they would be for the band ends travelling through the water. Those band ends mount a sub-pulley, so that will have some drag effect as well.

I only mention this aspect as on the stored energy analysis the rollergun seems to store less energy and has more parts to move than the two band conventional gun. Hydrodynamic drag during the shot is not included in that analysis, but whether it makes a difference I don't know.

"I only mention this aspect as on the stored energy analysis the rollergun seems to store less energy and has more parts to move than the two band conventional gun."

This ^^^^ MIGHT b an important statement. :rolleyes1:
Thank you popgun pete.

That said:
I love seals guns, his craftsmanship AND his love of rollerguns. Design passion is what drives many new products and innovations. Levers and wheels may have HUGE potential in spearguns. Levers and wheels even built pyramids back in the day. IMO, unconventional spearguns have great potential in spearfishing. Passionate people like seal, popgun pete, WoodGuy, phil, Tin Man, Dr. Maas, Don Paul, Art Pinder, etc, etc have given spearfishing sooooo much.

I probably don't have enough knowledge to actually comment on this thread but reading through the later parts of it I see some similarities to archery shooting. When building arrows for a bow, you have to match the spine of the arrow to the power of the bow. The "spine" being the stiffness of the arrow relative to the length of the arrow. If you have an arrow that is not stiff enough the energy causes side flex in the arrow. side flex causes huge accuracy problems and loss of speed. Im sure at some point, even though we are shooting steel shafts and not carbon or hollow aluminum arrows, this might hold true with spearguns as well. Meaning that we could add more bands or thicker bands until it has an adverse effect on our spears performance.

Thought #2: Again pulling from my days as an avid archery hunter and competitive shooter.
a lot of people get hung up on speed alone but the most important factor is actually kinetic energy. The formula to figure kinetic energy is M(mass of spear)x V2(velocity squared). Is there a way to figure the kinetic energy for your test? kinetic energy= penetration.

Last thought: Imagine the potential of a cam type system like a compound bow uses integrated in a roller set up.

ok now all you smart people can have the thread back.

The "Sea Archer" used a cam type system to duplicate the "let off" of a compound bow at full draw, it was a sort of Hawaiian sling with no trigger mechanism. It has been discussed on the Web, but the article may no longer be up as it has been a long time since I looked at it on the "rocknfish" web-site.